A test of what? It only makes sense to wait until June. Whether Cruz is here now or in June won't affect this season.
Whether and to what extent they are actually committed to a player-centric culture and building for the future. I think it's a loser's mentality to just write seasons off entirely, even if playoffs/hanging in the race/.500/pick your benchmark are all long shots.
They are also irrelevant to the player. Cruz looks like he is ready to handle the challenge of MLB pitching, and the more experience he gets now, the better off he'll be in terms of getting to the level he needs to be at to help the team compete next year and beyond. If he underperforms, you can always send him back down to AAA.
More specifically, though, I think it's a test in terms of the long term games that the front office will continue to play. Firmly committing to avoiding Super Two only makes sense if you are seeking above all else to only pay him pre-arb rates for the next three years. If he performs and you decide that you're willing to commit to him long-term, then the Super Two game is irrelevant.
I get that the front office/ownership is probably going to need to see some level of results before they hand out even team friendly long term deals. But even just hypothetically, Reynolds and Cruz could both be extended in the next 18 months, and Reynolds paid quite a bit in his highest years, and the payroll would still have plenty of room before it gets to the level of a serious, long-term and sustainable small market floor.
We still have to see what Cruz will do over the next 3-4 weeks, but if he's performing, then keeping him in AAA for extra games is a step backwards. Based on service, he can actually be called up within the next week and a half or two weeks and we'll gain the 7th year of automatic control unless he wins ROY. The only reason Super Two would even be a goal would be if we wanted to be paying him a rookie salary in 2025.
In any case, all this stuff is just mental gymnastics and hypotheticals. Cruz would be the third or fourth best hitter on the team and make them better immediately. Give him and Castillo a bunch of run and see what happens. The NL Central is bad enough that we'd likely hang around for longer than people think.